1. Field of the Invention
This invention broadly relates to supported catalysts for olefin polymerization and copolymerization.
2. Related Art
The art has sought to improve important material properties such as toughness, adhesion, surface properties (paintability and printability), solvent resistance, miscibility with other polymers, and rheological properties (1). Early transition metal Ziegler-Natta and metallocene type complexes are used extensively for the homopolymerization of α-olefins (2,3). The high oxophilicity of complexes based on Ti, Zr, and Cr causes them to be poisoned by most functionalized vinyl monomers, particularly commercially-available polar monomers such as acrylates, methacrylates, and vinyl acetate (1).
The development of olefin polymerization catalysts that are compatible with polar functionalized monomers is far from trivial, due to the strong interaction between polar monomers and catalysts, causing inhibition. A major advance was achieved by Brookhart et al. (4), who were the first to demonstrate the insertion copolymerization of ethylene and methyl acrylate (MA) using cationic Ni(II) and Pd(II) diimine complexes. The resultant polymer is branched with the acrylate units located only at the end of the branches (5-8). More recently, the random incorporation of acrylate monomers into linear polyethylene was reported by Drent et al. (9), who described the use of an in situ catalyst prepared by reaction of bis(ortho-methoxyphenyl)phosphinobenzene-sulfonate ligand in combination with Pd(dba)2 (dba=dibenzylideneacetone) with 2-17 mol % incorporation of acrylate monomers and relatively low molecular weights (Mn=2,000-20,000) (10,11). Theoretical studies suggest that the absence of ‘chain-walking’ by these catalysts is due to the increased barrier for β-hydride elimination relative to the Brookhart systems (12,13,14).
It has been proposed that appropriate electrophilicity of the metal center is required for copolymerization. Too high an electrophilicity results in undesired coordination of the polar functional group to the active site as a stable chelate, whereas too low an electrophilicity results in low reactivity for olefin insertion (15). Following the work of Pugh et al. (9), several groups have investigated the chemistry of Pd(II) phosphinobenzene-sulfonate systems and their performance in ethylene/acrylate and ethylene/CO copolymerization (16,17,18,19,20,21,22,23). In addition, these systems have been found to catalyze other copolymerizations, including vinyl acetate/CO (24), ethylene/norbornene (25), ethylene/functionalized-norbornene (26), ethylene/acrylonitrile (27), and ethylene/vinyl ether copolymerization (28,29), to produce linear copolymers. Insertion of acrylonitrile units into a linear polyethylene chain was also achieved with the neutral lutidine-based Pd(II) complexes. The reaction is slow, but occurs in a catalytic fashion (27). It has been suggested that a weak intermittent interaction of the methoxy group with the metal center could promote displacement of the coordinated, Lewis basic comonomer (30,31).
Neutral oxygen-containing Ni chelates as catalysts were developed many years ago by Keim el al. for the Shell higher olefins process (SHOP) (32) in which [P,O]Ni-catalyzed ethene oligomerization showed high tolerance for functional groups (33). Grubbs et al., developed a family of [N,O]Ni catalysts based on salicylaldimine ligands capable of copolymerizing ethylene with functionalized norbornenes (34). These catalysts, however, do not incorporate polar monomers with the polar functionality directly attached to the C—C bond. Subsequently, Carlini et al. introduced nickel salicylaldiminate catalysts, formed in situ, which were claimed to copolymerize ethylene with methyl methacrylate (MMA), producing high molecular weight linear copolymers (35). However, the likely formation of a mixture of homopolymers was not investigated. Gibson et al., employed [P,O]Ni catalysts to produce low molecular weight methyl methacrylate-terminated polyethylene (36). Ni catalysts based on phosphinobenzenesulfonate ligands have been synthesized and characterized by Rieger et al., and although activity for ethylene homopolymerization was reported (even in the presence of polar monomers), no copolymerization activity was observed (37).